Telephone system



Dec. 24, i935. H. HOVLAND TELEPHONE SYSTEM Filed June 9, 1954 9 Sheets-Sheet 1 QESOQ vn/EN TOR H Hol/AND BV MW g55/W1@ A T Tom/Ey Dea 24, 1935. H HOVLAND 2,025,389

TELEPHONE SYSTEM STEPd MA PG//VA L N QV /Nl/EN TOR H. Hol/AND ATT /VEV Dec. 24, 1935.

H. HOVLAND TELEPHONE SYSTEM Filed June 9, 1934 9 Sheets-Sheet 5 NNN /NVENTOR H. Hol/AND I BV ATTO EV Dec. 24, 1935. H. HOVLAND TELEPHONE SYSTEM Filed June 9, 1934 9 Sheets-Sheet 4 @7 A T TOR/VE? Dec. 24, 1935. H. HOVLAND 2,025,389

TELEPHONE SYSTEM Filed June 9, 1954 9 Sheets-Sheet 5 ooo oooo co0 Dork@ nooo mutua muzm IIIIIIIOIB um mula mmm 9 Sheets-Sheet 6 y ATTORNEY Dec. 24, 1935. H, HOVLAND TELEPHONE SYSTEM Filed June 9, 1934 Dec. 24, 1935.

H. HOVLAND TELEPHONE SYSTEM Filed June 9, 1934 9 Sheets-Sheet '7 N @Pm IIIIOID .xq

A TTOR/VEV Dec. 24, 1935. l

H. r-lovLn'mn` TELEPHONE SYSTEM Filed June 9, 1934 9 Sheets-Sheet 8 [hummm] Dec. 24, 1935.

H. HOVLAND TELEFHONE SYSTEM A TTORNEV Patented Dec. 24, 1935 UNITED STATES PATENT OFFICE Bell Telephone Laboratories,

Incorporated,

New York, N. Y., a corporation of New York Application June 9, 1934, Serial No. 729,737

17 Claims.

This invention relates to automatic telephone systems and more particularly to systems which include a main oice and one or more branch ofces.

The object of this invention is to provide a branch-cnice telephone system adapted for use under Widely varying traffic conditions, to increase the ilexibility and efficiency of the trunking, and to otherwise improve such systems.

In branch-oflice telephone systems it is desirable that connections between subscribers of the branch office be completed entirely through local switches. In such systems, the numbering scheme and trunking ordinarily necessitate the dialing of one, two or three digits of a called number before it is fully determined Whether or not the call is one requiring the use of main-cnice switches. Upon origination of a call in the branch ofce, the calling line is usually extended to a selector-repeater comprising a discriminating selector switch, an auxiliary trunking switch for selecting an idle trunk t-o the main oilice, and means for repeating impulses from the calling line over the trunk to operate selector switches in the main ofce. In response to the dial impulses incoming over the calling line, the discriminating selector operates in synchronism with a selector in the main oice, the brushes of the discriminating selector being restored to normal after -each digit prior to the one that completes determination of the route. The trunk to the main office is released or the branch-office switches rendered unresponsive to further dial impulses, as soon as the determination is completed. The discriminating selector is variously arranged to control the trunk-switching operation; in some cases shaft-operated level springs are provided, in some cases a vertical commutatcr and brush are provided, and in other cases a distinguishing potential is connected to a terminal of the rst set in one or more levels of the bank.

A feature of this invention is a digit-absorbing selector-repeater in which the trunk-switching operation is dependent upon the character of the terminals in the group selected in response to the last digit required for determining the route of the call. To this end a fourth brush is provided and additional terminals added to the bankof the discriminating selector. Such an arrangement permits the use of the absorbed digits for numbers in both the main and branch offices without increasing the complexity of the means for controlling the trunk-switching operation.

Another feature of the invention is a digitabsorbing selector-repeater which is arranged to repeat impulses to the main cnice and simultaneously repeat the same impulses to a succeeding selector of the branch oflice. This arrangement is necessary Where the route of the call is determined by two or more digits in addition to 5 the digits absorbed by the discriminating selector.

A further feature is a branch-cnice system in which a digit-absorbing selector-repeater simultaneously repeats impulses to the main ofiice and to a succeeding selector of the branch office and 10 in which the trunk-switching operation of the selector-repeater is determined by the character of the terminals in the group selected by said succeeding selector in response to the last of the digits which determine the route of the call. 15

A further feature of the invention is a branchofiice system in which special-service-code calls are completed through the main -ofce with the exception of reverting calls and calls to recordingcompleting toll boards, both of which are com- 20 pleted through switches in the branch office.

A further feature of the invention is a selectorrepeater arranged to operate an overflow register in case an idle trunk to the main oice has not been found prior to the receipt of the first dial 25 impulse.

The drawings which form a part of this specication represent in diagrammatic form a telephone system arranged in accordance with the features of this invention. Referring to the draw- 30 ings:

Fig. 1 shows schematically a subscribers station X and line 20, a line-finder LF having access to the line 2B, a selector-repeater SR permanently associated With the line-iin'der LF and comprising 35 a digit-absorbing selector switch BSI and a rotary trunk hunting switch TH, all of which equipment is located in a branch office.

Fig. 2 shows schematically a connector BC and a called subscribers station Y, a special-service- 40 code selector BSCS and an auxiliary specialservice-code selector BASCS, all oi which are located in the same branch oflice with the equipment shown in Fig. l.

Fig. 3 shows schematically a selector ISI in a 45 main oice to which TI, one of the trunks incoming from the branch office of Figs. l and 2, is connected. Fig. 3 also shows in schematic form a second selector SZ-A, a connector C and a subscribers station Z. Fig. 3 also shows an aux- 50 iliary rst selector ASI and a special-servicecode selector SCS.

Figs. 4, 5, 6, 7, 8 and 9 show various trunking arrangements for a main and branch-office system in which it is necessary to provide in the Y in which the subscribers are provided with dial impulse senders and the automatic switches used in establishing desired connections in accordance with the dial impulses are of the well known two-motion step-bystep type.V For a detailed description` of the structure and operation of switches of this type, reference may be had to pages 53 to 65 inclusive of the second edition of Automatic Telephony by Smith and Campbell published in 1921.

With the exception of the selector-repeater SR (including switches BSI and TH) of Fig, l, the connector BC and selector SCS of Fig. 2, and the selector ISI of Fig. 3, all of which are shown in detail, the Various automatic switches and associated apparatus are represented in the drawings by the enclosures within which the designations are placed, the set of brushes extending from the enclosures, and the associated sets of terminals.

Referring to Fig. 4, the trunking arrangement Yis designed to provide for a total of 7,800 four- Vdigit subscribers numbers in a main oilice and a branch cnice. Numbers from 2000 to 3999 inclusive and 4400 to 9999 inclusive are assigned to the main cnice and numbers from 4200 to 4399 inclusive are assigned yto the branch oiiice. It is apparent that it requires the dialing of a maximum of two digits to determine whether a called number is located in the branch or Vin the main oilice. The Vrst digit of thev branch-ofiice numbers night be, in another similar arrangement, any one of the digits except O or 1. The digit 0 is used for calling an operator and the digit 1 is employed only for special codes comprising three digits of which the rst two digits are 1l. A maximum of 700 numbers can be assigned to the branch oiice in which case there could be but 7100 numbers assigned to the main office.

In the branch oflice the subscribers lines terminate in line-finder switches such as LF and in the banks of connector switches such as BC. The line-finders are used to establish a connection with lines when calling and the connectors are used to establish a connection 'with lines when called. The station X represents the station of a calling subscriber andthe station Y represents the station of a called subscriber. Each line-finder is permanently associated with a selector-repeater such as SR which includes a selector switch BSI and a trunk-hunting switch TH. The terminals in the banks of the selector switches, such as BSI, are connected to succeeding selector or connector switches in the branch oflice or to trunks to an operator. The terminals in the banks of the trunk-hunting switches connect vto trunks, such as TI, leading to and terminating in incoming selectors, such as ISI, in the main oflice. The terminals of the rst level of the bank of the selector switches, such as BSI, are connected to special-service-code selectors such as BSCS; the terminals of the second and third levels are connected to connector switches such as BC; the terminals of levels 4 to 9 inclusive are vacant; and the terminals of the tenth or 0 level of the bank are connected to trunks leading to an operators position, either local or centralized. The Il operators position may therefore be in the main oiiice, the separate group of trunks from the tenth level of selector 5 BSI being provided instead of completing such calls through the tenth level of the incoming rst selectors in the main ofce so that the operator will know whether an incoming call originated in the main office or in the branch oiiice. If 10 special-service-code selectors are not provided in the branch office, the terminals of the first level would also be vacant. The terminals of the rst level of the specialservice-code selectors, such as BSCS, are connected to auxiliary special- 15 service-code selectors, such as BASCS; the terminals of the ninth levelconnect to reverting call selectors in the branch office; and the terminals of the tenth level connect to trunks leading to a toll recording-completing operators position. While direct trunks would not ordinarily be provided from the branch oflice for completing other Vspecial code calls, such trunks might be connected to the terminals of the other levels of the special-service-code selectors. To illustrate, 2 direct trunks might be provided for completing calls from the branch oflice to an information operators position; assuming the information operator code to be 113, these trunks would be connected to the third level of the special-service- 30 code selectors. The terminals of the iirst level of the auxiliary specialservicecode selectors, such as BASCS, are vacant but the terminals of all other levels are multipled to the terminals of the special-service-code selectors BSCS. 35 In the main ofce the subscribers lines may, in like manner, terminate in the banks of lineu iinder switches (none being shown) and in the banks of connectors such as C; the station Z represents a called subscribers station to which the 40 connector C has access. In addition to the incoming rst selectors such as ISI for extending callsoriginated by subscribers in the branch office, other first selectors (not shown) are provided for use in extending calls originated by subscribers 45 in the main oice. The rst selectors, both incoming and local, have access to the same or similar groups of trunks. The terminals of the rst level of the incoming selectors, such as ISI, are connected to auxiliary first selectors; the ter- 50 minals of the tenth level are vacant; the terminals of the fourth level are connected to second selectors represented by SZ-A; and the terminals of all other levels are connected to other second selectors represented by S2-B. The terminals 55k which are represented by selector S2-B are connected to connector switches thereby giving access to a total of 7000 subscribers lines. The terminals of levels 4 to 9 inclusive of the banks of 65 the second selectors which are represented by the selector S2-A, are connected to connector switches giving access to the remaining 600 lines in the main ofiice; the terminals of levels I, 2, 3 and i! of these second selectors are vacant. 70

The system disclosed in Figs. l, 2 and 3 conforms to the trunking arrangement of Fig. 4 and the operation of this system will now be described. The associated apparatus and circuit connections for selector-repeater SR, connector BC, special- 75 service-code selector BSCS and incoming vselector ISI are shown; but. the line-finder LF and all other selectors and connectors are represented by a set of brushes and one or more sets of terminals without showing the magnets, relays and other apparatus associated with each of these switches. The line-lnder LF may be similar to that disclosed in my Patent No. 1,711,682 granted May '7, 1929. The selectors ASI, SCS, St-A and Sii-B are substantially the same as the incoming selectoer ISI. The selector `BASCS is substantially the same as the selector BSCS and the main oflice connector C is substantially the vsame as the branch-oiice connector BC.

The selector-repeater SR is permanently associated with the line-finder LF and comprises a non-numerical rotary trunk-hunting switch TH, a two-motion selector switch BSl of the well known step-by-step type and associated control and switching apparatus. 'I'he switch TH in cludes the stepping-magnet 99, the brushes 9i, and 93 and the associated bank of terminals to which these brushes have access. The selector BSI includes the brushes 65, El, 68 and 6@ which have access to a bank of ten levels ofterminals, there being ten sets of terminals in each level; the terminal bank is represented by one set of terminals in each of the first, second, ninth and tenth levels. The terminals 'II of the nrst level are connected to a four-conductor trunk and il lustrate the condition Where nal determination of Whether the call is to be completed locally or over a trunk to the main oillce awaits the dialingA of one or more additional digits. The terminals 'i2 and 'IG of theV second and tenth levels are each connected to three-wire trunks and illustrate the condition when seizure of an idle trunk in such a level causes immediate release of the trunk to the main oice, the ground connected directly to the fourth terminals of each set of terminals 'm such a level being effective to cause the operation of a switching relay 25 to accomplish this result. The terminals I9 of the ninth level represent va cant levels and illustrate the condition where seizure of an idle trunk in such a level causes the return of the selector brushes to normal, the call being one which is completed through the main oiice; the resistance 80, through which the fourth terminal of each set of terminals in such a level is connected to ground prevents the operation of the switching relay 25. The selector BSi has a vertical-stepping magnet Ell, a rotary-stepping magnet SI, a release magnet 62, a set of vertical oi-normal springs VON, a set of 11th rotary step springs, a commutator brush $3, and a commutator 64 comprising a normal segment and ten oi-normal segments corresponding in position to the ten levels of the terminal bank. A terminal strip 65 is provided for connecting the coinmutator segments as required for use in any particular trunking and numbering arrangement.

The control apparatus for the selector-repeater SR includes a line relay 39, a release relay d3 and the aforementioned switching relay The all-trunks busy relays ill and 98 and register 99 common to a group of selector-repeaters are provided for registering the failure of switch TH to iind an idle trunk to the main oiiice.

Upon extension of the calling line through the brushes of line-finder LF to the selector-repeater SR, the switch TH operates to select and seize an idle trunk to the main oce. When thek Calling subscriber dials the first digit of a number, the impulses received by line relay 3D are effective to step the brushes of selector BSI up to a corresponding level and to repeat the impulses over the trunk to the main ofce. If the rst digit is 0, the brushes are then advanced step-b-y-step in the tenth level of the bank until an idle set of terminals is encountered, whereupon the operation of the switching relay 25 is effected to cause the release of the trunk to the main oflice and the extension of the calling line over the trunk connected to the seized set of terminals to an cperators position. If the first digit is any other than 0, the brushes of selector BSI are advanced to the corresponding level and immediately restored to normal. cates that the call is to be completed over the trunk to the main office, the impulses created by the dialing of the remaining digits of the called subscribers number are repeated over the trunk to the main oiice without causing further advance of the shaft and brushes oi" selector BSI. If the first digit alone is not suiiicient to indicate Whether or not the call is one which is completed over the trunk to the main office, the impulses created by the dialing of the second digit are repeated over the trunk to the main oiiice and also eifect the advance of the brushes of If the first digit alone indiselector BSi to a corresponding level; the brushes of selector BS! are then rotated to select an idle set of terminals in that level. After selector BS! has seized an idle set of terminals and if Vthe rst two digits finally determine that the call is to be completed over the trunk to they main omce as indicated by the connection of the fourth terminal of the selected set to ground through a resistance such as the resistance ist), the selector shaft and brushes are again restored to normal and succeeding trains of dial impulses are repeated to the main oiiice Without affecting further operation of selector BSI; but if the rst two digits finally determine that the trunk to the main oiice is not required for completion of the call as indicated by the connection of the fourth terminal of the selected set in the bami of switch BSI directly to ground,'this trunk is released and thD calling line is extended directly through the brushes of selector BSl and the seized set of terminals to a succeeding switch in the branch oflice. If the rst two digits are insumcient to determine whether. the call is to be completed locally or over the trunk to the main office, such, for instance, as is the case when the first two digits are 11, the third train of impulses is repeated over the trunk to the main cflice and also repeated through the brushes of selector BSI to a special-service-code selector BSCS in the branch oice; if the third digit is either 0 or 9, seizure of an idle set oi terminals in the selected level of the selector BSCS eiiects the operation of the switching relays of the selector-repeater SR to release the trunk to the main ofce, the special-service-code selector BSCS having direct access to toll recording trunks (code and to reverting call selectors (code 119). Should a preliminary impulse have preceded the code 110 or 119, the special-servicecode selector BSCS is advanced to the hrst level by the single impulse comprising the third train oi impulses and seizure of an idle set of terminals in this level extends the call to an auxiliary speoial-servicecode selector BASCS. 'I he selector BASCS extends the call to a toll recording trunk or a reverting call selector upon the further dialing of 0 or 9. Y

Whenever all trunks to the main oiice are busy, a busy tone is transmitted to the calling station after the dialing of the rst digit. An

' al1-trunk Vbusy condition encountered by the sleeve conductor'24 thereby causing the operation of relay 35 of the selector-repeater SR. 'I'he circuit for energizing relay 35 is traced from battery through the winding of this relay, upper back contact of relay 36, inner lower back contact of relay 33, uppermost back contact of relay 50, inner lower back contact of relay 49, conductor 2B and through the inner lower back con-V tact of relay 25, over conductor 24 to the ground at the start relay (not shown) of line-finder LF. Relay 35 closes a circuit from battery through the winding and interrupter contacts of stepping magnet 90 of trunkehunting switch TH, through the winding of relay 33, to ground at the inner lower front contact of relay 35. The magnet 90 is marginal and does not operate in series with the Winding of relay 33 but relay 33 operates in this circuit unless the trunk to which the brushes of switch TH are connected is busy, in which case the winding of relay 33 is short-circuited by the busy ground potential on the sleeve terminal of the busy trunk. The shortcircuiting connection is traced from the interrupter contacts of magnet 90 through the lowermost front contacts of relay 35, and the lowermost back contact of relay 33 to the sleeve brush 93 of switch 'II-I. If brush 93 is in contact with the grounded sleeve terminal of a busy trunk, the magnet 90 is operated to step the brushes tothe next set of terminals. As soon as an idle trunk is encountered, the ,lack of ground potential. on the sleeve terminal permits the operation of relay 33, the magnet 90 being insufficiently energized to cause further advance of the switch TH. With relay 33 operated, the sleeve terminal of the selected trunk is connected to ground at the lowermost front contact of relay 33 as a Vguarding potential to prevent seizure of the same trunk by other trunk-hunting switches similar to TH. Relay 33 closes a holding circuit for relay 35 which is traced from battery through the winding of relay 35, upper back contact of relay 36, inner lower front contact of relay 33, lower back contacts of the 11th rotary step springs and Vthrough the middle lower back contact of relay 25 to the ground potential on conductor 24.

When the brushes 2|, 22 and 23 of line-nder vLF have been advanced into engagement with the set of terminals to which the line 20 is connected, the line relay 30 of the selector-repeater SR operates due to the energization of its windings in a circuit which is traced from battery through its lower winding, lower back contact Vof relay 28, lowermost back contact of relay 25,

brush 22 of line-nderLF, over line 20 and through the telephone instrument at station X, back through brush 2|, uppermost back contact of relay 25, upper back contact of relay 28, upper winding of relay 30, upper back contact of the 11th rotary step springs, lowermost back contact of relay 49, lower back contact of relay 50V and through the right winding of the dialtone transformer 53 to ground. The operation of relay 30 closes a circuit from battery through the Winding of relay 43, inner lower back contact of relay 45, inner upper -back contact of relay 44, lower front contact of relay 30, conductor 29 and through the middle upper back contact of relay 25 to ground. Relay 43 connects ground through its inner upper front contact to sleeve conductor 24 to hold the line-finder switch LF and thence through brush 23 to hold the cut-off relay (not shown) of the line 20 in the well known manner. Relay 43 also closes a circuit from battery through the upper winding of relay 40 and inner lower front contact of relay 43, over conductor 29, to ground at the middle upper back contact of relay 25; but the energization of the upper winding of relay 40 is insuicient to operate this relay until its lower winding is also energized by current in the aiding direction.

YThe aforementioned operation of relay 30 also closes a bridge across the line conductors of the trunk TI, which was seized by the operation of relay 33 thereby causing the operation of the line relay 20| of the associated incoming selector ISI in the main office. The circuit for operating relay V20| is traced fromV battery through the upper winding of relay 20|, inner lower back contact of relay 204 over one conductor or trunk TI, brush 92 of switch 'I'H in the branch oce, inner upper front contact of relay 33, upper front contact of relay 30, outer upper front contact of relay 35, winding of relay 38, lower winding of relay 40, uppermost-back contact of relay 3|, uppermost front contact of relay 33, brush 9| of switch TH over the other conductor of trunk TI, inner upper back contact of relay 204, lower winding of relay 20| to ground at Vthe upper back contact of the 11th rotary step springs of switch ISI. The operation of relay 20| closes an obvious circuit for operating relay 202. No further actionV takes place until the calling subscriber dials the first digit of the number of the station with which a talking connection is desired.

When the calling subscriber dials the rst digit of a number, relay 3 is alternately released and reoperated each time the impulse contacts of the dial are opened and closed,that is, as many times as there are units in the digit dialed. Relay 43, being slow in releasing, remains operated dur-- ing the receipt of each train of dial impulses by relay 30. The impulses are repeated by the upper contacts of relay 30 to cause the alternate release and reoperation. of relay 20| of the incoming selector ISI in the main oice. The release of relay 30 in response to the first impulse closes a circuit from battery through the winding of relay 3| conductor 54, lowermost front contact of relay 43, back contact of relay 30 over conductor 29 to ground at the middle upper back contact of relay 25; it also closes a circuit from battery through the winding of vertical-stepping magnet 60 in parallel with battery through the winding and inner upper back contact of relay 50, through theupper back contact of relay 49, lowermost back contact of relay 45, conductor 54, lowermost front contact of relayV 43, back contact of relay 30 and over conductor 29 to the ground at relay 25. Relays 3| and 50 and magnet 60 are thereby operated. The operation of magnet 60 steps the shaft and brushes of switch vBSI up to the rst level of the terminal bank.

I'he operation of relay 3| closes a short-circuit around the winding of.relay 38 and lower windell) ing of relay 40; since relay 3| is slow in releasing, this short-circuit remains closed until all of the impulses in a train have been received, the current over the trunk to the main office being thereby increased to insure the reoperation of relay 20| of incoming selector ISI between impulses. 1Relay 50 locks through its upper front contact, inner lower back contact of relay 00, over conductor 26, through the inner lower back contact of relay and over conductor 24 to the holding ground potential at relay 43. At its lower continuity contacts, relay 50 substitutes a direct ground connection for the connection through the right-hand winding of dial-tone transformer 53. Should relay 33 not yet havebeen operated when dialing begins due to the failure of switch 'II-I to find an idle trunk, relay 35 releases when relay 50 operates thereby preventing further trunk hunting on the part of switch TH. When relay reoperates at the end of the rst dial impulse. magnet 60 releases. Each succeeding release and reoperation of relay 30 in response to the impulses generated by the dialing of the first digit, cause a corresponding operation and release of magnet 60 resulting in the elevation of the brushes of selector BSI to the correspondingly numbered level of the terminal bank. The VON springs of selector BSI are actuated as soon as the shaft and brushes are moved out of their normal position thereby closing a circuit from battery through the winding or relay d0, middle contacts of the VON springs, back contact of the rotary-stepping magnet 6I, conductor 56, upper back contact of relay 45, lower front contact of relay 3|, conductor 31, inner lower front contact of relay 43 over conductor 20 to ground at the middle upper back contact of relay 25. Relay d8 operates and locks through its own inner front contact under control of the magnet 6I to the same ground.

If the first digit is either 2, 3, 5, 6, 7, 8 or 9, and the selector-repeater is arranged in accordance with the trunking and numbering scheme of Fig. it is immediately determined upon receipt of the first train of impulses that the called line is located in the main oiiice or can be reached only by routing the call through the main oiiice. The release of relay 3l, after all of the impulses in the first train have been received, closes a circuit from battery through the winding of relay 4e, terminal I3 of terminal strip 65 through the conductors connecting terminal I 3 to terminals 3, 8, 7, 5, 5, 3 and 2 of the same terminal strip, and from any one of the latter mentioned terminals through that one of the correspondingly numbered segments of commutator 60 with which commutator brush 63 is in contact, through brush 63, upper back contact of relay 02, back contact of release magnet 62, lower back contact of relay 3|, conductor 3l, inner lower front contact of relay 43 over conductor 29 to ground at the middle upper back contact of relay 25. Upon closure or" this circuit, the operation of relay 40 causes the release of relay 50 and the operation of release magnet The circuit for operating release magnet 62 is traced from battery, through the winding of this magnet, lower contacts of the VON springs over conductor 59, lower back contact of relay 44 to ground at the upper front contact of relay t0. 'I'he operation of magnet 62 causes the shaft and brushes of the selector to be returned to normal position. Relay 43 remains operated, being locked through its inner lower front contact over conductor 26, through the inner lower back contact of relay 25 to ground on sleeve conductor 24. The impulses created by the dialing o-f the remaining digits of the called subscribers number are repeated by the upper contacts of relay 30 over the trunk lTI to the main oflice. 5

In case relay has released prior to the operation of relay 49 on account of no idle trunk to the main office having been found by switch TH before the dialing of the rst digit, a trunksbusy tone is transmitted to the calling station, the 10 upper conductor of line 20 being connected through the upper winding of line relay 30, through the upper back contact of the 11th rotary step springs, the lowermost front contact of relay Q3, the upper back contact of relay 35, 15 over conductor 96, through the winding of relay Sl and through the right winding of the busytone transformer i6 to ground. Relay 9T operates, closing a circuit for operating relay 98 and the operation of relay 98 closes a circuit for 20 operating the trunks-busy register 99. Upon the receiver being replaced at thevcalling station, the line relay 30 releases. Relay 43 then releases, thereby disconnecting the holding ground from sleeve conductor 2li to cause the release of the 25 cut-off relay (not shown) of the calling line and the holding relay (not shown) of the line-finder LF. The line-finder LF is thereupon returned to normal in the usual well known manner. Relay 49 also releases when the holding ground is dis- 30 connected from sleeve conducto-r 24, the selectorrepeater SR being normal in readiness for use on another call.

Assuming the trunk TI to have been seized as hereinbefore described, the line rel-ay 20| of the 35 incoming selector ISI 'in the main oice responds to the first train of impulses repeated by line relay 30 of selector-repeater SR in the branch office to advance the brushes 2||, 2I2 and 2I3 to the corresponding level of the terminal bank, 40 the first level of which is represented by the set of terminals 22| and the second level of which is represented by the set of terminals 222. The. release of relay 20| upon receipt of the first repeated impulse closes a circuit from battery through the winding of the vertical-stepping magnet 206, winding of relay 203, lower front contact of relay 202 and back contact of relay 20| to ground at the uppermost back Contact of relay 200. The current in this circuit operates 'magnet 206 and relay 203. The operation of magnet 206 steps the brushes of lswitch ISI up to the first level of the terminal bank. When the shaft of the selector switch moves out of its normal position, the vertic-al .off-normal springs VON are actuated, thereby closing'a circuit for operating relay 205 from battery through the winding of this relay, upper contacts of the VON springs, front contact of relay 203 to ground at the uppermost front contact of relay 202. Relay 205 closes a holding circuit for itself which includes the contacts of the rotary-stepping magnet 201 and its own upper front Contact to the ground at the uppermost back contact of relay 200. When relay 20| reoperates at the end of 65 the rst impulse, magnet 206 releases. Each succeeding release and reoperation of relay 20| causes a corresponding operation and release of magnet 206 thereby stepping the brushes 2|I, 2I2 and 2I3 up to the desire-d level of the bank. 70 Relay 203 is slow in releasing and remains operated until all of the impulses corresponding to the first digit have been received. Relay 202 is also slow in releasing and remains operated during the receipt of impulses by relay 20|. The 75 rele'ase of relay 203,` after the last impulse of the rst digit has been received, closes a circuit vfor operating the rotary-stepping magnet 201; this circuit is traced from battery through the winding of magnet 201, lower front contact of relay 205, back contact of relay 203 to ground at the upper iront contact of relay 202. The operation of magnet 201 advances the brushes 2| I, 2 I2 and 2i3 into engage-ment with the first set of terminals in the previously selectedY level. Relay 205 releases when magnet 201 operates and the release of relay'205 causes the release of magnet 201. VlIf the rst set of terminals is idle, no further operation v'of magnet 201 occurs; but if test brush 2|3 encounters a ground potential on the terminal which it engages, which potential indicates that this set of terminals is busy, relay 205 reoperates in a circuit from battery through its winding, upper contacts'of the VON springs, back Contact of magnet 201, conductor 2 I0, lowermost back contact of relay 204, through test brush 2|3 to the grounded terminal. A parallel circuit pathY extends from'conductor 2 I0 through the windingof relay 204, the lower contacts of the 11th rotary step springs to ground at the upper front contact of relay 202; but relay 204 is short-circuited and ydoes not operate Vif the rst set of terminals is busy.` The reoperation of relay 205 recloses the circuit for operating magnet 201,'the brushes 2||, 2|2 and 2|3 being thereby advanced to the next set of terminals.

VRelay 205 and magnet 201 repeat their cycle of operations until the brushes engage an idle set of terminals at which time relay 204 operates in series with the winding of rel-ay 205; being marginal relay 205 does not reoperate. The op eration of relay 204 connectsA the ground at the upper front contact of` relay 202, through the lowermost front contact of relay 204 and through brush 2|3 to the test terminal of the selected set to guard this set of terminalsY against seizure by any other selector. Relay 204 disconnects the incoming line conductors of trunk TI from the windings of line relay 20| and extends these conductors through brushes 2||. and 2| 2 to the line conductors of the selected trunk. VRelays 20| and 202 release, the ground for holding relay operated being supplied in usualmanner from the succeeding selector to 'which the seized set of terminals is connected.

Ii the rst digit is any other than 1 or 0, the connection over trunk TI is extended through a set of terminals represented by the terminals .222, to a second selector S2-A. Upon receipt of the next train of impulses repeated over trunk Tl, the selector S2-'A operates to select the corresponding level and tovhunt for and seize an idle trunk which leads to a connector such as C. The'conne'ctor C operatively responds successively to theV next two trains of impulses repeated over trunk Ti; Ythese impulses correspond to the last two digits of the called number and cause the completion of the connection to the called subscribers'line. The called line is tested'in the vusual manner to determine whether it is idle or busy. `If busy, a busy-tone is Ytransmitted to the calling subscriber in the usual m-anner. If idle, ,a ringing circuit isclosed to signal the called station; and, upon removal oi the receiver thereat,

`the' talking circuit is established between the calling and called stations, all inthe usual and well known manner.

leases causing thev return of the Iine-nder LF .and selector-repeater SR to normal as hereinbefore described. The release of relay 30 also causes the release of the line relay (not shown) of the connector C, the holding ground being thereby disconnected from the sleeve conductor of selectors SZ-A and ISI in the main oiiice to cause their return tc norm-al in the usual manner. The connector C is also returned to normal in the usual manner upon the receiver at the called station being placed upon the receiver hook.

If the first digit, dialed by the subscriber at station X is 4, the calledV line may bein the branch oiTice or in the main oflice. In this case, the release of relay 3| closes a circuit for operating relay 4|; this circuit is traced vfrom battery through the winding of relay 4|, uppermost back contact of relay 34, terminals I5 and'4 of terminal strip 65, segment 4 and commutator brush 63, upper back contact of relay 42,.back contact of release magnet 62, lower back contact of relay-3|, inner lower front contact of relay 43, conductor 20, to ground at the middle upper back contact of relay 25. Relay 4| closes a circuit for operating relay 42. Relay 4| also closes a circuit for operating release magnet 62, from battery through the winding of magnet 62, lower contact of the VON springs, inner lower back contact of relay 34, inner lower front contact of relay 4|, lower back contact of the 11th rotary step springs, uppermost front contact of relay 43, to ground at the inner upper front contact of relay 43. The operation of magnet 62 opens the operating circuit for relay 4|, this relay now being held operated by a locking circuit from battery through its winding and uppermost front contact, winding of relay 34, upper contact of the VON springs, conductor 55, inner lowerback contact of relay 49, conductor 26, and through the inner lower back contact of relay 25 to the holdn ing ground on sleeve conductor 24; the winding of relay 34 is also operatively energized in this circuit. The shaft and'selector brushes 05 to Y69 inclusive and commutator brush 63 are restored to normal due to the operation of release magnet 62. The magnet 62 and relays 4| and 34 are thereby released; relay 42 remains operated on account of the locking circuit through its Winding and inner lower front contact, over conductor through the inner lower back contact of relay 49 to the Vsleeve conductor holding ground' as hereinbefore traced. When the second digit isY dialed, relay 30 responds as hereinbefore described to cause the advance of brushes 66 to 69 inclusive and commutator brush 63 up to the corresponding level and to repeat the'impulses over trunk Tl. The second operation of the VON springs closes a circuit for operating relay 48 from battery through the winding of relay 48, middle contacts of the VON springs, back contact of the rotary-stepping magnet 6|, overconduotor 58, through the uppermost Vback contact of relay 45, lower front contact of relay 3l, conductor t1, inner lower front contact of relay 43, conductor 29 to ground at the middle upper back contact oj relay 25. When relay 3| releases at the end of the second train of dial impulsesythe rotarystepping'magnet 6| is energized in acircuit from battery through Vits winding, lowermost front contact ofrrelay 42, lowermostV back Ycontact of relay 4| uppermost front contact of Vrelay/48', lower back contact of relay 3|, conductor 31, thence as above described to ground at the baci: Contact of relay 25. The operation of magnet 6| steps the brushes 66, 61, 68 and 69 into engagement with the first set of terminals in the level corresponding to the second digit dialed. The operation of magnet (il causes the release of relay 48 and the release of relay 48 causes the release of magnet 8l. If this rst set of terminals is busy, a guarding ground potential on the test terminal is connected through brush Eli,v inner upper back contact of relay 25, middle lower back contact of relay 49, uppermost back contact of relay 45 to conductor 58 to reoperate relay 48. This busy ground potential is also elective to shortcircuit the winding of relay 45. Relay 48 again closes the circuit for operating magnet 8l thereby advancing the brushes to the next set of terminals. Relay 48 and magnet 8l thus repeat their cycle of operations to advance the brushes one step at a time until an idle set of terminals is reached; whereupon relay 45 operates, its winding being energized in a circuit from battery through the winding of relay 48, middle contact of the VON springs, back contact of magnet 6l, conductor 58, .winding of relay 45, upper front contact of relay 42, inner lower back contact of relay 4l, lower back contact of the 11th rotary step springs, over conductor 21, through the uppermost front contact of relay 43, and over conductor 24, to the holding ground at the inner upper front contact of relay 43. Relay 48 is marginal and does not operate in series with the winding of relay 45. If all trunks happen to be busy, the brushes are advanced beyond the tenth set of terminals and the 11th rotary step springs become operated, thereby causing the successive release of relays 35 and 33 and the connection of they right winding of busy-tone transformer 48 through the front contact of these springs to the upper winding of line relay 38 to transmit a busy-tone to the calling station.

Assuming that the first digit dialed is 4 and that the second digit dialed is any other than O, 1, 2 or 3, the terminal engaged by brush 60 is permanently connected to ground through a re.- sistance such as the resistance 80 associated with the set of terminals 19 representative of the ninth level of the terminal bank. In this case, with relay 45 operated, a circuit is closed from battery through the Winding of relay 44, lower winding of relay 25, middle upper front contact ci relay 45, through brush 69 and resistance 80 (or a similar resistance) to ground. Relay 44 operates but relay 25 being marginal does not operate due to resistance 80. Relay 44 closes a circuit for operating relay 49 from battery through the winding of relay 49, lower front contact of relay 44, over conductor 28 and through the inner lower back contact of relay 25 to holding ground on conductor 24. Relay 49 locks through its inner lower front contact to the same ground and causes the release ofA relays 42 and 50. The release of relay 42 causes the release of relay 45 and the release of relay 45 causes the release of relay 44. The release of relay 44 closes a circut for operating release magnet 82 from battery through the Winding of magnet 62, lower contacts of the VON springs, lower back contact of relay 44 to ground at the upper front contact of relay 49. The shaft and brushes of the selector switch of the selector-repeater YSR, are thereby restored to normal. The impulses created by the dialing of the remaining digits are repeated by relay 30 over trunk Tl to the main oflice to complete the connection to the'called station.

If the iirst digit dialed is 4 and the second digit dialed is 2 or 3, the terminal engaged by brush 89 of selector BSE, upon seizure of an idle set of terminals in the corresponding level is connected directly to ground and the aforementioned operation of relay 45 is, in this case, effective to cause the operation of the marginal relay 25 as well as the operation of relay 44. Being somewhat slow in operating, relay 49 remains normal. Relay 25 closes a locking circuit from battery through its upper Winding and inner upper front Contact to the holding ground on conductor 24. The operation of relay 25 causes the release of relays 30 and 43, the release of relays 42, 45 and 44, and the release of relay 50. Relay 25 also extends the talking conductors of line-finder LF through brushes 86 and 61 to the succeeding branch olce switch which is connected to the seized set of terminals. Assuming the seized set of terminals to be connected to the connector switch BC, line relay ll of this switch operates, closing a circuit for operating the release relay 02; and relay lil?. connects ground through its lowermost front contact over sleeve conductor l, through brush 68 and the middle upper front contact of relay 25 to sleeve conductor 24 thereby maintaining a holding ground on this conductor after the release of relays 38 and 43. The linerelay llil of connector BC responds to the impulses created by the dialing of the last two digits of the called number. The rst release of relay l0l closes a circuit from battery through the winding of the vertical-stepping magnet l l winding of relay lil, normally closed contacts of the vertical off-normal springs VON, upper front contact of relay l8r., to ground at the back contact of relay lill. The operation of magnet ll4`3 steps the brushes lll, H2 and ll3 up to the first level of the terminal bank thereby operating the VON springs; the circuit for energizing magnet l I4 and relay H33 is now traced through the front contact of relay 03 and the lower front contact of the VON springs. The reoperation of relay llll at the end of the rlrst impulse causes the release of magnet H4, Each succeeding release and reoperation of relay llll in response to additional impulses in the same train causes/the reoperation and release or magnet H4 to advance the brushes to the level corresponding to the digit dialed. Relay l0? is slow in releasing and remains operated during receipt of dial impulses. Relay |03 is also slow in releasing so that it remains operated until the last impulse of the train has been received. When the rst impulse of the train corresponding to the last digit of the called number is received by relay l0 l a circuit is closed from battery through the winding of 'rotary-stepping magnet H5 and lower back contact of relay l88 in parallel with battery through the winding of relay l05, then through the inner back contact of relay l0?, back contact of relay |03, lower front contact of the VON springs, and through the upper front contact of relay |02 to ground at the back contact of relay lill. The rotary-stepping magnet l l5 operates to advance the brushes lll, H2 and H3 into engagement with the first set of terminals in the selected level and relay 05 operates to con'nect the winding of vtest relay |01 to the sleeve or test brush l l3. The upper front contact of relay it maintains the energization of this relay and magnet H5 independently of the inner back contact of test relay lll'l. The reoperaticn ci relay ll at the end of the rst impulse of the last train causes the release of magnet H5. Each succeeding release and reoperation of relay l0! in response to impulses created by the dialing of the final digit of the called number causes the operation and release of magnet II to advance the brushes I II, II2 and H3 into engagement with the corresponding set of terminals. Relay |05, being slow in releasing, remains operated between impuluses and long enough after the brushes III, II2 and II3 have engaged the terminals of the called line to insure the operation of test relay |01 if the test terminal is connected to ground due to the line being busy. If relay |01 operates, it locks through the inner back Contact of relay |05 and its own lower front contact to ground at relay |02. The operation of relay |01 connects the right winding of busy-tone transformer I I0 through its upper con- Y tact to the lower talking conductor of the conergization of its upper winding in this circuit v tact. of relay |06 and through the lower winding Y Y of relay suiciently to close its inner lower front contact and thus energize its lower winding in a circuit over conductor II1 to ground at the inner lower front contact of relay |02. Relay |08, when fully operated, connects a'holding ground through its lowermost front contact'to the Ysleeve brush II3 to hold the cut off relay of line |29 operated and vcloses a signaling circuit from the ringing current source II8, through Vthe uppermost front contact of relay |08, upper winding and lower back contact of the tripping relay |06, middle lower front'contact of relay |08, brush II2 over the line and through the ringer at station Y, back through brush I I I and the inner upper front contact of relay |08 to ground at the upper back contact of relay |06. When the receiver is removed at station Y to answer the call, relay Y |06 operates, closing a locking circuit from battery through its lower winding and inner lower front contact over conductor I|1 to ground at relay |02. With relay |06 operated, talking current is supplied to the called station Y in a circuit from battery through the upper winding of relay |04, through the uppermost front contact of relay |06, the inner upper front contact of relay |08, brush III, over the called line |20 and through station Y, back through brush I I2, middle lower front contact of relay |08, lowermost front con- I04 to ground. Relay |04 operates thereby connecting ground through its lowermost front contact to Vconductor I I1 so as to hold relays |09 and |08 operated until relay |04 also releases Yin case the connection is released by the calling Y station before it is released by theVV called station.

VRelay |04 also reverses the connection between Y the calling line and the windings of relay IOI as a supervisory indication that the call has been answered.` The talking current .is transmitted Vthrough condensers |00.

The release of relay IOI- causes the release of relay |02 thereby disconnecting the holding ground from conductor |09. Relay' 25 of the selector-repeater SR, the holding relay (not shown) of the line-finder LF, and the Ycut-ofi? relay (not shown)V of the calling line 20 are thus released and the line-lnder LF is thereupon restored to normal in the usual manner. The release of relay closes a circuit for operating the release magnet 62 to restore the selector BSI to normal. The circuit for operating magnet 62 is traced Vfrom battery through the winding or magnet 62, lower front contact of the VON springs, conductor 59, lower back contacts of relays 43 and 30, to ground at the middle upper back Contact of relay 25. Restoration of springs VON when the selector reaches normal, opens the circuit through the winding of release magnetv 62. The release of both relays |02 and |04 of the connector BC causes the release of relays |06 and |08 and the operation of release magnet |6 whereby the connector switch is restored to normal in the usual manner. Y

If the rst digit dialed by the calling sub- 20 scriber is O, to obtain connection with an operator, the brushes of selector BSI are advanced up to the tenth level. Upon release of relay 3| a circuit is closed from vbattery through the winding of relay 42, inner upper back contact of relay 2e 34, segment I0 of commutator 64 and brush 63, upper back Contact of relay 42, back contact of release magnet 62, lower back contact of relay 3|, conductor 31, inner lower front contact of relay 43, over conductor 29 torground at relay 25.

Y Relay 42 operates in this circuit and closes a locking circuit as hereinbefore described. Relay 48 having been operated by the actuation of the VON springs, the operation of relay 42 closes the circuit for energizing the rotary-stepping magnet 6I as hereinbefore described. The brushes 66, 61, 68 and 69 are advanced into engagement with the rst setof terminals in the O level of selec- 'tor BSI. If the iirst set of terminals is busy, relay 48 and magnet 6| effect the further advance of the brushes until an idleV set of terminals is reached and relay is operated as hereinbefore described. The terminal with which brush 66 is in contact being connected directly to ground, relays 275 and 44 both operate and the 45 connection is extended over the trunk which Vis connected to the seized set of terminals to the O operators position. This trunk circuit (not shown) is arranged so that the release of the connection is controlled jointly by the operator and 50 the calling subscriber. (If no trunk wereprovided directly from the branch office to the O. operators position, the terminal with which brush 69 is in contact would be connectedto ground through .a resistance soas to cause the opera,u tion of relay 44 without causing the operation of relay 25; in this case relay 49 is operated and the call isV completed 'over the main-oiiice trunk, through the KO level of the incoming selector ISI, over a trunk to an operators position, the 00 brushes of selector BSI being restored to normal as hereinbefore described.)

If the calling subscriber dials a special service three digit code, the iirst two digits of which Y are 11, the brushes of incoming selector ISI in Vthe main oice and the brushes of selectonBSI 63, upper back contact of relay 42, back contact of magnet 62, lower back contact of relay 3|, inner lower front contact of relay 43, to ground at the middle upper back contact of relay 25. This circuit is opened by the operation of magnet 62 but the winding of magnet 62 is held operated until the shaft of selector BSI reaches its normal position by a circuit from the winding of magnet .62, through the lower contacts of the VON springs and front contact of magnet 62, through the lower back contact of relay 3|, conductor 3l, inner lower front contact of relay 43, conductor 26, to ground at the middle upper back contact cf relay 25. When the shaft and brushes of switch BSI reach normal, this circuit is opened at the VON springs but magnet 62 is now held operated in a circuit which includes the inner lower front contact of relay 56, lower winding and inner back contact of relay 41, front Contact of magnet 62, lower back contact of relay 3|, thence to the ground at relay 25. Relay i? operates sufliciently to close a circuit through its upper winding and front contact, over conductor 55, through the inner lower baci; contact of relay 49, over conductor 26, to the holding ground on conductor 24. The current through the upper winding of -relay 4l completes the operation of this relay, thereby causing the release of magnet 62. The dialing of the second digit of the number 110 or 119 once again advances the brushes of selector BS| to the first level; the repeating of the impulse created by the dialing of the second digit 1 over trunk T l to the main ofce causes the operation of the auxiliary first selector ASI in the main oice to select an idle trunk in the rst level leading to a special-service-code selector SCS. Relay 42 of selector-repeater SR is operated, as soon as relay 3| releases, by the current in a circuit which includes Athe lower front contact of relay 4T, lowermost back contact of relay 34, segment I and commutator brush 63, thence to ground at relay 25 as above traced. The inner lower front contact of relay 42 closes before this operating circuit is opened at the upper back Contact of relay 42 so that relay 42 locks through its inner lower front contact and the inner lower back .contact of relay 40, over conductor 25 to the holding ground on conductcr 26. Relay 48 having been operated, as hereinbeiore described, the operation of relay 42 starts the rotary trunk-hunting operation of selector BSL Upon seizure of `an idle trunk in the rst level,'relay 45 is operated thereby connecting the windings of relays 44 and 25 in series to brush 63 as hereinbefore described. Relays 44 and 25 do not operate since the selected set of terminals are connected to a special-service-code selector such as BSCS. Relay 45 closes a circuit from ground at the middle upper back contact of relay 25, conductor 29, Alower front Contact of relay 30, inner upper back contact of relay 54, inner lower front contact of relay 45, resistance 39, brush 5l of selector BSI, middle upper back contact of relay |54 of selector BSCS, and through the upper winding of line relay 55| to battery. Relay |5| operates, closing a circuit operating the release relay '|52. Relay |52 f contact, over sleeve conductor |59, through brush 55, inner upper back contact of relay 25, middle lower back contact o1 relay 46, uppermost front ccntact of relay @5, to the sleeve conductor 24 of the selector-repeater; relay |52 also connects ground through its inner upper front contact,

the upper normally closed contact of the 11th rotary step springs, uppermost back contact of relay |54, brush 66 of selector BSI, inner upper front contact of relay 45, uppermost back contact of relay 44, through the winding of release relay 43 of selector-repeater SR to battery; relay 43 is thus held operated under control of the succeeding selector in the branch oice. The response of relay to the impulses created by the dialing of the third digit of the special three digit code is effective to repeat these impulses through its lower front contact to the line relay |5| of the special-service-code selector BSCS in the branch office and through its upper front contact to the line relay of the specialservice-code selector SCS in the main olce. The release of line relay I5I of selector BSCS closes a circuit from battery through the winding of vertical-stepping magnet |60, winding of relay |53, lower front contact of relay |52, back contact of relay |5l, to ground at the inner upper back contact of relay |54. Magnet |60 operates, advancing the shaft and brushes to the rst level of terminals. The VON springs are actuated when the shaft moves out ouf its normal position and with relay |53 operated, a circuit is closed from battery through the winding of relay |55, upper contact of the VON springs, front contact of relay |53, over conductor |59, to ground at the upper front contact of relay |52. Relay |55 locks independently of the continued operation of relay I 53 through the back contact of the rotary-stepping magnet I6| and the upper front contact of relay |55. The reoperation of relay |55 at the end of the rst impulse causes the release of magnet |60. Each succeeding release and reoperation of relay I 5| in response to the third digit dialed by the calling subscriber causes a corresponding operation and release of magnet to advance the brushes up to the desired level of the terminal bank. Being slow in releasing, relay |52 remains operated during the receipt of dial impulses by relay |5I. Relay |53 is also slow in releasing and remains operated until the last of the train of impulses has been received by relay |5I. When relay |53 releases, a circuit is closed from battery through the winding of rotary-stepping magnet I6|, lower front contact of relay |55, back contact of relay |53 over conductor |59 to ground at relay |52. The operation of magnet I6| steps the brushes |66,

|61, |68 and |65 into engagement with the first' set of terminals in the selected level. The operation of magnet I6| causes the release of relay |55 and the release of relay |55 causes the release of magnet itl. If the trunk connected to the rst set of terminals is busy, a ground potential is encountered by brush |68 thereby causing the reoperation of relay |55 and magnet I6|. The circuit for reoperating relay |55 is traced from battery through its winding, upper contact of the VON springs, back contact of magnet |6|, lower back contact of relay |54, through brush |68 to the busy ground potential. As long as brush |68 encounters a busy ground potential, relay |55 and magnet I6| repeat their cycle of operations. When an idle trunk is found, relay i5@ operates due to the energization of its winding in a circuit from battery through the winding of relay |55, upper contact of the VON springs, back contact of magnet I6|, winding of relay |54, lower back contact of the 11th rotary step springs to ground at relay |52. If the third digit dated is any other than 1, 9 or 0, the terminal with which brush |69 is in engage- Vlector SCS in the main office having been advanced to that oneof the levels 2 to 8, inclu- *to a line the ring conductor of which becomes Y(code`119).

sive, which corresponds to the third digit dialed, the call is completed over an idle trunk in this level to Va special service operator or to an intercepting operator if the coderdialed is not in use.

'If, however, the third digit dialed is 9, the terminalwith which brush |69 is in engagement is connected directly to ground thereby causing the operation of both of relays and 44 of .selector-repeater SR; the main ofce trunk is thereupon released and the calling line is conl nected through brushes 65 and 61 of selector BSI,

thence through the upper front contacts of relay |54 and through brushes |66 and |61 of the special-service-code selector BSCS to a trunk which terminates in a reverting call selector If the third digit dialed is 0 (code 110), the brushes of selector BSCS are raised to the tenth level thereby immediately connect- Relays 2 5 to cause release of the trunk to the main oice before the main-office service-code selector SCS has selected an idle trunk in its tenth level.

Should a preliminary impulse have accidentally preceded the dialing of the service codes 110 or 119, the brushes of switch BSCS are also advanced to the first level and an idle trunk selected in thislevel to extend the call to an auxiliary special-service-code selector represented by BASCS which is in all respects similar to the switch BSCS except that theterminals of the iirst'level connect to trunks to an intercepting operator. All other levels of the bank of switch BASCS are multiplied to the corresponding levels j of the switch BSCS.

If the trunking arrangement of Fig. 4 is modiiied by omitting special-service-code selectors in the branch oflice so that reverting calls (code 119) and toll recording calls (code 110) are completed through the main oice, numbers from BSI and the call is completed over a trunk to the main office; Y

Incase a selector-repeater becomes connected toa line which is permanently short-circuited or permanently grounded, a permanent signal alarm circuit (not shown) is closed by the incoming first selector in the main-office in well known manner. To transfer the permanent sig- 'or in the branch office.

nal indication from the main oice to the branch oflice and free the trunk to the main ofce, the maintenance attendant in the main oiiice opens the connections between the conductors of the trunk and the line relay of the incoming selector and connects battery through not more than 200 ohms resistance to the tip conductor of the trunk thereby operating relay 36. Relay 36 locks through its lower winding and front Contact to the holding ground on conductor 24 and causesl the release of relays 33 and 35. Relay 3B also connects ground to the conductor connecting to the alarm apparatus 52 thereby causing a permanent signal condition to be indicated in the branch oilice. Relay 35 is slow in operating so that it does not operate when relay 3| releases after the dialing of each digit and before relay 38 has had time to reoperate or when relay 38 releases momentarily due to the Vusual reversal of current over the trunk when the called subscriber answers. If the trunk selected by switch TH is open, a permanent signal condition on the calling line is ineffective to cause the operation of the permanent signal indicator in the main oflice. Y

Referring to Fig. 5, the trunking arrangement provides for a total of eight thousand tive-digit subscribers numbers in a main oflice and a branch office, all of these numbers having the digit 4 as the rst digit. Numbers from 42000 to 43999, inclusive, are assigned to the branch oiiice and numbers from 44000 to 49999, inclusive, are assigned to the main office. The branch ofiice is equipped with special-service-code selectors for completing toll recording and reverting calls. The commutator connections and the terminal bank arrangement for the selector BSI of the selector-repeater SR are the same for the trunk-V ing arrangement of Fig'. 5 as for the trunking system of Fig. 4. As in the system represented in Fig. 4, the selector-repeater SRis arranged to absorb onedigit and the dialing of a maxlmum of two digits is required t'o determine whether a called number is located in the main Since the line numbers are five-digit numbers, third selectors are provided in both the main and branch oices. In the branch oflice, the selector switch BSI of the selector-repeater SR has access through the terminals in the second and third levels of its bank to third selectors whichare represented by BSt. The branch-ofiice third selectors have access through all levels of their banks to connectors which are represented by BC. In the main olce the incoming selectors, represented by ISI, have access through the terminals of the rst level t0 auxiliary rst selectors through the terminals of the fourth level to second selectors which are represented by S2, and through the terminals of all other levels except the tenth level to incoming selectors inother oices of the system. The second selectors have access through the terminals of levels 4, 5, 6, 1, 8 and 9 to third selectors, such as S3; and the third selectors S3 have access to connectors which are represented by C. The operation of a system arranged as shown in Fig. 5 is similar to the operation of the system disclosed in Figs. 1, 2, 3 and 4 except that on branch oflice calls a third selector is included in the connection. The operation of the branch-office third selector BS3 is similar to that of the mainoiiice selector ISI.

^ Referring to Fig.V 6, the trunking arrangement provides for a total of eight thousand five-digit subscribers numbers in a main and a branch offlce, all of these numbers having the digit 4 as the rst digit. Numbers from 42000 to 42099, inclusive, and from 42600 to 42999, inclusive, are assigned to the branch oice and numbers from 42100 or 42599, inclusive, and from 43000 to 49999, inclusive, are assigned to the main oiiice. Numbers having any one of digits 2, 3, 5, 6, 7, 8 or 9 as the first digit are assigned to subscribers in other oices of the system, calls to such oiilces being routed through the main ofiice shown. Special-service-code selectors are provided in the branch ofce for completing toll recording and reverting calls. The cross connections for the commutator segments of selector-repeater SR are the same for the trunking arrangement of Fig. 6 as for the trunking arrangement of Fig. 4, as shown in Fig. 1. The terminals of levels I, 2 and 0 of selector switch BSI are` connected the same for the trunking arrangement of Fig. 6 as are the terminals of these levels for the trunking arrangement of Fig. 4 as shown in Fig. l; and the terminals of levels 3 to 9, inclusive, are con nected the same as shown for the terminals of level 9 in Fig. l. The branch-oilice third selector BSS of Fig. 6 is similar to the special-service-code selector BSCS shown in Fig. 2 except that the fourth or control terminal of the sets of terminals in levels I, 2, 3, 4 and 5 are connected to ground through a resistance such as resistance 80 in Fig. l; and the control terminal of the sets of terminals in levels 6, 1, 8, 9 and Il are connected directly to ground. The selector-repeater SR is arranged toabsorb one digit and the dialing of a maximum of three digits is required to determine Whether a called number is located in the branch oiiice or is to be completed over a trunk to the main office. If the rst digit of the number dialed is any other than 0, l or 4, it is immediately determined that the call is for a subscriber in some office other than the branch and main ofiices and is to be completed over a trunk to the' main oiiice; the switch BSI is, therefore, immediately restored to normal and rendered nonresponsive tov further dialing, the dial impulses ci the succeeding digits of the called number being repeated over the trunk to the main cnice. If a special-service-code 11X (X being any digit from 0 to 9) is dialed, the call is completed as hereinbefore described for similar calls in the system represented in Fig. 4. [If the digit 0 is dialed, the call is completed over a trunk from the tenth or Il level of the bank of switch BSI, the trunk to the main oice being immediately released. If the rst digit of the number dialed is 4, the selector BSI is restored to normal and the incoming selector ISI extends the connection through a set of terminals in the fourth level to an idle second selector S2. If the next digit dialed is any other than 2 the selector BSI is restored to normal a second time and rendered non-responsive to further dialing, the call being for a station located in the main office; but if the next (second) digit dialed is 2, the selectors BSI and S2 are each advanced to hunt for an idle trunk in the second level of their banks; the trunk selected by BSI leads to a branch-ofiice third selector BSS and the trunk selected by the mainoiiice selector S2 leads to a main office third selector S3--A. The impulses corresponding to the next (third) digit of the number dialed, are repeated over the trunk to the main oihce to selectively operate the third selector S3-A and are also repeated over the trunk selected by switch BSI to operate the branch-office third selector BSS. The brushes of each of selectors BSS and S3-A are thereby stepped up to the level corresponding to the third digit and then automatically advanced from one set of terminals to another in that level until an idle trunk is encountered. If this third digit is l, 2, 3, 4, or 5, the potential encountered by the fourth or control brush of the selector BSB is such as to cause the release of switches BSI and BSS, and the connection is extended through the brushes of selector S3-A and an idle trunk in the selected one of levels I, 2, 3, 4 or 5 to a connector switch C. The switch C then responds to the dialing of the last two digits of the number of the called station to complete the desired connection. If the brushes o1 selector BS3 are advanced to one of levels 6, l, 8, 9 or Il, the potential encountered by the fourth or control brush of this selector is such as to cause the release of the trunk to the main office, the connection being extended through the brushes of selector BS3 and the selected trunk to a connector switch BC. The connector BC responds to the dialing of the last two digits of the called subscribers number to complete the desired connection.

Referring to Fig. 7, the trunking arrangement provides for a total of 9800 ve-digit subscribers' numbers in a main and a branch oiice, all of these numbers having the digit 8 as the rst digit. The numbers from 82200 to 82599, inclusive, are assigned to the branch office: the numbers from 80000 to 81999, inclusive, and from 82600 to 89999, inclusive, are assigned to the main oiiice. Special-service-code selectors are provided in the branch ofce for completing toll recording and reverting calls. The selectorrepeater SR is arranged to absorb two digits and the dialing of a maximum of three digits is required to determine whether a called number is located in the branch oflice or is to be completed over a trunk to the main ofiice. The segments of the commutator of switch BSI of selector-repeater SR are connected as shown in Fig, 10. The terminals oi levels I and Il of selector BSI are connected the same for the trunking arrangement of Fig. 'I as for the trunking arrangement of Fig. 4 as shown in Fig. 1; the terminals of levels 2, 3, 4 and 5 of selector BSI are connected the same as shown for level 2 in Fig. 1; and the terminals of levels 6, l, 8 and 9 are connected the same as shown for level 9 of Fig. l. If the iirst digit dialed is any other than 0, 1 or 8, it is immediately determined that the call is for a subscriber in some office other than the branch and main oiiices and is to be'completed over a trunk to the main office; the switch BSI is thereupon restored to normal and rendered non-responsive to further dialing, the dial impulses of the succeeding digits of the called number being repeated over the trunk to the main oflice. If the rst -digit is 0 the call is completed over a trunk from the tenth or 6 level of the bank of switch BSI, the trunk to the main oflice being immediately released. 1f one of the three-digit specialservice codes having l I for the first two digits is dialed, the selector-repeater SR operates as hereinbefore described for a similar call in the system shown in Figs. 1, 2, 3 and 4. If the rst digit dialed is 8, selectors BSI and ISI are advanced to the eighth level and relays 4I and 34 of the selector-repeater SR are operated, as hereinbefore described when the rst digit is 4 on a call in the system according to Fig. 4; but in this case, relay di does not cause the immediate operation of relay 2. When the second digit is dialed (8 having been the rst digit) selectors 

